The present invention is directed to the upgrading of synthesis gas to alcohols. In particular, the present invention is directed to a novel catalyst having a high selectivity to the manufacture of alcohols from synthesis gas.
Since the oil crises of 1973 and 1978, the general price of oil has increased at a rapid rate. As a result of this price increase, chemicals derived from petroleum have become increasingly expensive. Accordingly, alternative sources for use as raw materials in the production of these chemicals have been sought. Synthesis gas is one of the sources being actively pursued as an alternative to petroleum in the production of many chemicals.
Two main types of processes have been proposed for the preparation of alcohols from synthesis gas. First, the modified Fischer and Tropsch synthesis with catalyst and second, the modified methanol synthesis. The present invention is directed to the improvement in the Fischer-Tropsch process.
As a rule, processes of the Fischer and Tropsch type have poor selectivity and productivity. Catalysts which possess acceptable activity in this process generally tend to give a wide spectrum of products, for example, hydrocarbons and oxygenated hydrocarbons having a broad distribution of carbon atom contents. This not only complicates the recovery of desired products, but results in the waste of reactants to commercially uninteresting by-products. Present research has been directed at alleviating these problems.
Recently, in an article by Inoue entitled "Alcohol Synthesis from Syngas on Ruthenium-based Composite Catalysts", Applied Catalysis, 11 (1984), pp. 103-116, a ruthenium-molybdenum-sodium supported catalyst is disclosed as useful in the synthesis of alcohols from syngas. In addition, U.S. Pat. Nos. 4,478,955; 4,377,643 and 4,476,247 to Pesa et al disclose ruthenium-copper based catalysts useful in upgrading of synthesis gas. The alkali promoted ruthenium-copper catalyst of the Pesa et al patents produce very little methanol. The higher oxygenates produced are primarily carboxylic acids or aldehydes and an additional hydrogenation step is necessary to arrive at a mixed higher alcohol product. Accordingly, a disadvantage of this patent is the requirement for a second step to produce the higher alcohols. Promotion of the ruthenium-copper system with some Group VIII metals, notably rhodium and iridium, caused the selectivity to shift toward the higher alcohols and away from the acids, but the activity was severely reduced and almost entirely directed to the production of methanol. In addition, the use of rhodium and iridium dramatically increases the costs associated with the process. Accordingly, improvements in the catalyst system disclosed in the Pesa et al patents are desired. Applicants' process and catalyst are directed to an improvement in this system.